Many imaging devices, such as printers, photocopiers, and multi-function imaging devices, store a supply of media sheets, such as paper sheets, in one or more internal trays. The sheets are vertically stacked within the trays by a user or service technician. Media trays are sized and configured to hold hundreds or thousands of sheets. In many printers, a single media tray is configured with adjustable structure to enable the tray to accept stacks of media sheets in various sizes. For example, a single media tray can accept letter, A4, and legal sized sheets, among other sizes. The printer operates in different print modes to form images on each size of media sheets.
Some printers accept manual input from an operator to identify the size of media sheets stored in the media tray. Manual identification may be inconvenient, however, for the operator, and if the size of media sheets in the media supply is misidentified, then the printer may malfunction during operation. Other printers identify the size of media sheets prior to printing on the media sheets using one or more sensors that are located within the media supply. For example, sensors in the media supply can identify both the length and the width of media sheets before the printer starts printing images on the media sheets. Some existing printers can verify if a media sheet is approximately the same as the media sheet sizes indicated by the media supply sensors using one or more sensors in the media path during a print job. If a media sheet is substantially smaller than the size indicated by the sensors in the media supply, the printer can suspend or cancel the print job until the media supply is filled with the appropriately sized media sheets.
While existing media supplies can identify the size of media sheets, the sensors in the media supplies also have drawbacks. For example, media supply trays are often implemented as slideable trays that are opened and closed frequently to replenish paper in the printer. Sensors located in the media tray can be damaged or misaligned during continued use of the media tray. Additionally, sensors located in the media supply increase the cost of manufacturing the media tray and may decrease the reliability of the printer. Consequently, printers that identify the sizes of media sheets used in the printer more robustly would be beneficial.